This invention relates generally to lower leg prostheses and, more particularly, to lower leg prostheses configured to duplicate the performance characteristics of the natural human foot and ankle.
Significant advancements in the field of lower leg prostheses have been made in recent years, due largely to the development of composite materials technology. Lower leg prostheses incorporating fiberglass/epoxy and carbon fiber/epoxy composite materials have been developed, which closely duplicate the performance characteristics and feel of the natural human foot and ankle.
One such lower leg prosthesis is sold by CRP, Inc. d/b/a Springlite, under the name Advantage Low Profile. That prosthesis incorporates a flexible lower plate and a relatively rigid upper plate, which are attached together by an intermediate elastomeric layer. A toe portion of the lower plate projects beyond a forward end of the upper plate, and a heel portion of the lower plate projects beyond a rearward end of the upper plate. The lower and upper plates are formed of a high-strength, carbon fiber/epoxy composite material, and the elastomeric layer is formed of a high-density polyurethane material. An attachment pyramid is mounted on the upper plate, for attaching the lower leg prosthesis to a socket for receiving the amputee""s residual limb or to an intermediate prosthesis such as a pylon. A crepe sole can be attached to the underside of the lower plate, and a foam foot shell or cosmesis can be placed over the plates, to provide the prosthesis with an appearance of a natural human foot.
The Advantage Low Profile prosthesis described briefly above has enjoyed substantial commercial success. Nevertheless, it is believed that the prosthesis can be improved upon by providing greater stability during use, particularly at heel strike and at toe-off, and also by providing a greater degree of multi-axial movement, thus coming closer to duplicating the performance and feel of the natural human foot and ankle. The present invention fulfills these needs and provides further related advantages.
The present invention is embodied in an improved lower leg prosthesis that, during use, provides an improved feel at heel strike and that provides improved inversion/eversion compliance. The prosthesis includes an upper foot plate, a forefoot plate, and a heel plate, all aligned along a longitudinal axis. An intermediate elastomeric layer is disposed between the upper and lower plates, for attaching the plates together. This elastomeric layer is configured to allow the forefoot and heel plates to move substantially independently of each other, relative to the upper foot plate.
In more detailed features of the invention, the forefoot and heel plates together have a toe section, a mid-foot section, and a heel section, and those two plates are separated from each other by a gap located in the mid-foot section. The elastomeric layer includes an anterior section disposed between the upper foot plate and the forefoot plate and a posterior section disposed between the upper foot plate and the heel plate, with a gap being defined between the anterior and posterior sections, adjacent to the gap between the forefoot and heel plates. The gap between the forefoot and heel plates preferably has a substantially uniform width, in the range of about 1 to 12 mm. The gap between the anterior and posterior sections of the polyurethane layer preferably has a substantially circular cross-section that blends smoothly with the lower surface of the upper plate and with the upper surfaces of the forefoot and heel plates.
The forefoot plate, heel plate, and upper foot plate all are preferably formed of a composite material incorporating high-strength fibers or filaments, e.g., carbon fiber or fiberglass, and they are configured to be flexible in directions along the longitudinal axis. The forefoot plate can have a thickness that varies along its length, from a maximum at its anterior end to a minimum at its posterior end, and the heel plate likewise can have a thickness that varies along its length, from a minimum at its anterior end to a maximum at its posterior end. The upper foot plate can have a thickness that tapers to a minimum at its anterior end.
The elastomeric layer preferably incorporates a solid, high-density polyurethane. It has a preferred thickness of at least about 2 mm. In the case of applications that do not incorporate a pylon built into the upper foot plate, the elastomeric layer most preferably has a thickness that ranges from about 2 cm adjacent to the forefoot plate, to about 3 cm adjacent to the heel plate. On the other hand, in the case of prostheses that do incorporate a pylon built into the upper foot plate, the elastomeric layer most preferably has a thickness that ranges from about 0.5 cm adjacent to the forefoot plate to about 8 cm adjacent to the heel plate.
In a separate and independent feature of the invention, the forefoot and heel plates together constitute a lower foot plate having a periphery that extends beyond the periphery of the upper plate, and the elastomeric layer extends fully over a substantial portion of that lower foot plate""s upper surface, including to a substantial portion of the lower foot plate""s periphery. The lower foot plate could, in this feature of the invention, be formed as a single component. The portion of the elastomeric layer portion that extends beyond the upper foot plate""s periphery preferably has a uniform thickness of at least about 2 mm.
Other features and advantages of the present invention should become apparent from the following description of the preferred embodiments, taken in conjunction with the exemplary drawings, which illustrate the principles of the invention.